diff --git a/src/Makefile b/src/Makefile
index 596ad5a..025acfa 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,11 +1,7 @@
-all: test-bitmap
+all:
 
 %.o: %.c
 	gcc -O0 -Wall -Wextra -pedantic -ggdb $< -o $@
 
-test-bitmap: test-bitmap.c bitmap.c
-	gcc -Wall -Wextra -pedantic -g -ggdb test-bitmap.c bitmap.c -o test-bitmap
-
 clean:
 	rm -f *.o
-	rm -f test-bitmap
diff --git a/src/bitmap.c b/src/bitmap.c
index 6753e79..ea79eac 100644
--- a/src/bitmap.c
+++ b/src/bitmap.c
@@ -20,14 +20,14 @@
 int bitmap_compare(bitmap *a, bitmap *b)
 {
   uint16_t row = 0;
-  uint16_t bit = 0;
+  uint16_t diff = 0;
   size_t  cnt = 0;
 
   for (row = 0; row < 16; row++) {
-    bit = 1 << 15;
-    while (bit) {
-      cnt += !!(((*a)[row] & bit) ^ ((*b)[row] & bit));
-      bit >>= 1;
+    diff = (*a)[row] ^ (*b)[row];
+    while (diff) {
+      cnt += (diff & 1);
+      diff >>= 1;
     }
   }
 
diff --git a/tests/Makefile b/tests/Makefile
new file mode 100644
index 0000000..42a2f16
--- /dev/null
+++ b/tests/Makefile
@@ -0,0 +1,10 @@
+all: test-bitmap
+
+CFLAGS=-Wall -Wextra -O0 -g -ggdb -pedantic
+
+%.o: %.c
+	gcc $(CFLAGS) $< -o $@
+
+SRC=../src/bitmap.c bitmap.c
+test-bitmap:
+	gcc $(CFLAGS) $(SRC) -o $@
diff --git a/tests/bitmap.c b/tests/bitmap.c
index 24a6097..3021ed3 100644
--- a/tests/bitmap.c
+++ b/tests/bitmap.c
@@ -1,5 +1,5 @@
-#include "main.h"
-#include "bitmap.h"
+#include "../src/main.h"
+#include "../src/bitmap.h"
 
 int
 main(int argc, char **argv)